michael@0: /*
michael@0:  * Copyright 2014 Google Inc.
michael@0:  *
michael@0:  * Use of this source code is governed by a BSD-style license that can be
michael@0:  * found in the LICENSE file.
michael@0:  */
michael@0: 
michael@0: #ifndef SkDynamicAnnotations_DEFINED
michael@0: #define SkDynamicAnnotations_DEFINED
michael@0: 
michael@0: // This file contains macros used to send out-of-band signals to dynamic instrumentation systems,
michael@0: // namely thread sanitizer.  This is a cut-down version of the full dynamic_annotations library with
michael@0: // only the features used by Skia.
michael@0: 
michael@0: // We check the same define to know to enable the annotations, but prefix all our macros with SK_.
michael@0: #if DYNAMIC_ANNOTATIONS_ENABLED
michael@0: 
michael@0: extern "C" {
michael@0: // TSAN provides these hooks.
michael@0: void AnnotateIgnoreReadsBegin(const char* file, int line);
michael@0: void AnnotateIgnoreReadsEnd(const char* file, int line);
michael@0: }  // extern "C"
michael@0: 
michael@0: // SK_ANNOTATE_UNPROTECTED_READ can wrap any variable read to tell TSAN to ignore that it appears to
michael@0: // be a racy read.  This should be used only when we can make an external guarantee that though this
michael@0: // particular read is racy, it is being used as part of a mechanism which is thread safe.  Examples:
michael@0: //   - the first check in double-checked locking;
michael@0: //   - checking if a ref count is equal to 1.
michael@0: // Note that in both these cases, we must still add terrifyingly subtle memory barriers to provide
michael@0: // that overall thread safety guarantee.  Using this macro to shut TSAN up without providing such an
michael@0: // external guarantee is pretty much never correct.
michael@0: template <typename T>
michael@0: inline T SK_ANNOTATE_UNPROTECTED_READ(const volatile T& x) {
michael@0:     AnnotateIgnoreReadsBegin(__FILE__, __LINE__);
michael@0:     T read = x;
michael@0:     AnnotateIgnoreReadsEnd(__FILE__, __LINE__);
michael@0:     return read;
michael@0: }
michael@0: 
michael@0: #else  // !DYNAMIC_ANNOTATIONS_ENABLED
michael@0: 
michael@0: #define SK_ANNOTATE_UNPROTECTED_READ(x) (x)
michael@0: 
michael@0: #endif
michael@0: 
michael@0: #endif//SkDynamicAnnotations_DEFINED